<DKIM> [BUG] function argument set to an object

[Nicolas Sebrecht]

On Mon, Dec 19, 2016 at 07:06:17AM +0000, Luke Kenneth Casson Leighton wrote:
> aiyaaa!  mustn't do this!  it's the "pattern" for a singleton:
> 
> LocalStatusSQLite.py (and probably LocalStatus.py as well):
>     def savemessage(self, uid, content, flags, rtime, mtime=0, labels=set()):
> 
> 
> example:
> 
> >>> def singleton(val, x = set()):
> ...     x.add(val)
> ...     return x
> ...
> >>> singleton(5)
> set([5])
> >>> singleton(7)
> set([5, 7])
> 
> baad, veryverybaad :)  so, any time that labels are used, if you
> happen *not* to have that last argument in calling savemessage but
> there are instances where it is, things go horribly badly wrong
> because the labels= argument ends up STORING prior labels in that
> set()...
> 
> 
> must do this instead:
> 
> >>> def notasingleton(val, x=None):
> ...     if x is None:
> ...             x = set()
> ...     x.add(val)
> ...     return x
> ...
> >>> notasingleton(5)
> set([5])
> >>> notasingleton(7)
> set([7])
> >>> y = set()
> >>> notasingleton(7, y)
> set([7])
> >>> notasingleton(5, y)
> set([5, 7])
> 
> will submit a patch later, am in the middle of the first lmdb revision.

Looks correct analisys to me. I didn't check how this issue impacts the
code, though.

-- 
Nicolas Sebrecht